<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .A {
      width: 100px;
      height: 100px;
      margin-bottom: 10px;
      background-color: red;
    }
  </style>
  <style>
    .B {
      width: 100px;
      height: 100px;
      margin-top: 20px;
      background-color: blue;
    }
  </style>
</head>
<body>
  <div class="A">A</div>
  <div class="B">B</div>
</body>
</html>